1. Field of the Invention
The invention relates to a method and apparatus for controlling automatically the lens aperture of any still camera although it is particularly useful in the single-lens reflex type. The exposure control is a feed-back mechanism which supplies information about the present iris setting value to a device for changing the iris setting value if object brightness so requires.
2. Description of the Prior Art
In previous EE automatic exposure cameras, the iris value was determined by clamping the existing reading on an ammeter with combtooth. Cameras of this type have been variously improved and put to practical use with the limitation that they have low mechanical integrity due to the ammeter, which cannot be avoided.
There have been previously proposed systems in which aperture control is by means of a closed loop; an electric signal corresponding to the iris value is detected as a resistance value by the variation of relative position of a variable resistor and a brush which interlocks with an iris value decision member or an iris driving member. The difficulty in these systems is that the movement of the contact point between the resistance body and the brush is carried out at a speed much higher than normal for a variable resistor; the results being that contact portions severly wear and extraneous noise is generated. Therefore, it is extremely difficult to produce such an apparatus which has a high reliability and durability.
It is therefore an object of this invention to provide a stable apparatus having a high reliability and durability while overcoming those disadvantages as noted above, and the fundamental concept of the invention is to obtain an electric signal corresponding to the iris value by the provision of a contactless structure.